U.S. patent application number 11/034036 was filed with the patent office on 2005-06-09 for methods and compositions for overcoming resistance to biologic and chemotherapy.
Invention is credited to Shepard, H. Michael.
Application Number | 20050123983 11/034036 |
Document ID | / |
Family ID | 21998430 |
Filed Date | 2005-06-09 |
United States Patent
Application |
20050123983 |
Kind Code |
A1 |
Shepard, H. Michael |
June 9, 2005 |
Methods and compositions for overcoming resistance to biologic and
chemotherapy
Abstract
This invention provides a method for identifying potential
therapeutic agents by contacting a target cell with a candidate
therapeutic agent which is a selective substrate for an endogenous,
intracellular enzyme in the cell which is enhanced in its
expression as a result of selection by biologic or chemotherapy.
This invention also provides methods and examples of molecules for
selectively killing a pathological cell by contacting the cell with
prodrug that is a selective substrate for an endogenous,
intracellular enzyme. The prodrug is subsequently converted to a
cellular toxin. Further provided by this invention is a method for
treating a pathology characterized by pathological,
hyperproliferative cells in a subject by administering to the
subject a prodrug that is a selective substrate for an endogenous,
overexpressed, intracellular enzyme, and converted by the enzyme to
a cellular toxin in the hyperproliferative cell.
Inventors: |
Shepard, H. Michael; (Rancho
Santa Fe, CA) |
Correspondence
Address: |
BINGHAM, MCCUTCHEN LLP
THREE EMBARCADERO CENTER
18 FLOOR
SAN FRANCISCO
CA
94111-4067
US
|
Family ID: |
21998430 |
Appl. No.: |
11/034036 |
Filed: |
January 12, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11034036 |
Jan 12, 2005 |
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09789226 |
Feb 20, 2001 |
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09789226 |
Feb 20, 2001 |
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09130839 |
Aug 7, 1998 |
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6495553 |
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60055525 |
Aug 8, 1997 |
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Current U.S.
Class: |
435/6.16 ;
435/7.23; 514/269; 514/49 |
Current CPC
Class: |
A61P 35/02 20180101;
C07H 19/10 20130101; A61K 31/7068 20130101; G01N 2333/91011
20130101; A61K 31/513 20130101; A61K 31/7072 20130101; C12Q 1/48
20130101; C07H 19/06 20130101; A61P 35/00 20180101; C12Q 1/485
20130101; A61P 43/00 20180101; G01N 33/5011 20130101 |
Class at
Publication: |
435/006 ;
435/007.23; 514/049; 514/269 |
International
Class: |
C12Q 001/68; G01N
033/574; A61K 031/7072; A61K 031/513 |
Claims
1-36. (canceled)
37. A method for identifying potential therapeutic agents,
comprising: contacting a target cell with a candidate therapeutic
agent that is a selective substrate for a target enzyme, under
conditions that favor the incorporation of the agent into the
intracellular compartment of the target cell; and assaying the
target cell for inhibition of cellular proliferation or cell
killing.
38. A method for selecting a uridine analogue for reducing or
inhibiting the replication or spread of tumor cells, comprising the
steps of: providing a uridine analog unsubstituted in the
5-position; testing said uridine analog for activation by
thymidylate synthase; and selecting said uridine analog when found
to be activated by thymidylate synthase.
39. The method according to claim 38, wherein the testing step
comprises: measuring cytotoxicity of said uridine analogue with
respect to at least one cell line with a high expression of
thymidylate synthase enzyme and at least one cell line with a low
expression of thymidylate synthase enzyme; and the selecting step
comprises: selecting said uridine analogue when the cytotoxicity
measured with respect to the at least one cell line with a high
expression of thymidylate synthase enzyme is greater than the
cytotoxicity measured with respect to the at least one cell line
with a low expression of thymidylate synthase enzyme.
40. The method according to claim 38, wherein the uridine analog
contains a radioisotope.
41. The method of claim 38 wherein the uridine analogue is a
compound of the following general formula: 6wherein: A=N, C; B=H,
hydroxyl, halogen, acyl (C.sub.1-C.sub.6), alkyl (C.sub.1-C.sub.6),
alkoxy (C.sub.1-C.sub.6); D=O, S, NH.sub.2; and G=substituted or
unsubstituted cyclic sugar, substituted or unsubstituted acyclic
sugar, substituted or unsubstituted mono, di, or
tri-phospho-cyclic-sugar phosphate; substituted or unsubstituted
mono, di, or tri-phospho-acyclic-sugar phosphate; substituted or
unsubstituted mono, di, or tri-phospho-cyclic sugar analogues;
substituted or unsubstituted mono, di, or tri-phospho-acyclic sugar
analogues wherein the substituents are alkyl (C.sub.1-C.sub.6),
alkoxy (C.sub.1-C.sub.6) or halogen.
42. The method according to claim 41, wherein the compound contains
a radioisotope.
43. A method of imaging an organism, comprising the steps of:
contacting the organism to be imaged with a compound of the
formula: 7wherein: A=N, C; B=H, hydroxyl, halogen, acyl
(C.sub.1-C.sub.6), alkyl, alkoxy (C.sub.1-C.sub.6); D=O,
S,NH.sub.2; E=H, alkyl, substituted alkyl, alkenyl, substituted
alkenyl, alkoxy, substituted alkoxy, halogen, or any substituent
which is readily cleaved in the body to generate H, alkyl,
substituted alkyl, alkenyl, substituted alkenyl, alkoxy,
substituted alkoxy, or halogen; at least one of W, X, Y, Z is a
label or a label containing moiety having sufficient isotopic
activity for imaging and the remainder of W, X, Y, Z=H, hydroxyl,
halogen, alkyl (C.sub.1-C.sub.6), substituted alkyl
(C.sub.1-C.sub.6), alkoxy (C.sub.1-C.sub.6), substituted alkoxy
(C.sub.1-C.sub.6); J=C, S; and K=O, C; and imaging the
organism.
44. A method of determining the proliferation rate of a tissue,
comprising the steps of: contacting the tissue with a compound of
the formula: 8wherein: A=N, C; B=H, hydroxyl, halogen, acyl
(C.sub.1-C.sub.6), alkyl, alkoxy (C.sub.1-C.sub.6); D=O,
S,NH.sub.2; E=H, alkyl, substituted alkyl, alkenyl, substituted
alkenyl, alkoxy, substituted alkoxy, halogen, or any substituent
which is readily cleaved in the body to generate H, alkyl,
substituted alkyl, alkenyl, substituted alkenyl, alkoxy,
substituted alkoxy, or halogen; at least one of W, X, Y, Z is a
label or a label containing moiety having sufficient isotopic
activity for imaging and the remainder of W, X, Y, Z=H, hydroxyl,
halogen, alkyl (Cl-C.sub.6), substituted alkyl (Cl-C.sub.6), alkoxy
(Cl-C.sub.6), substituted alkoxy (C.sub.1-C.sub.6); J=C, S; and
K=O, C; imaging the tissue; and determining the amount of the
compound incorporated into the tissue, wherein the amount of the
compound incorporated into the tissue correlates to the
proliferation rate of the tissue.
45. The method of claim 44, wherein the compound is a labeled
uridine analog.
46. A method of assessing the response of tumors to treatment with
a thymidylate synthase inhibitor, comprising the steps of: (a)
administering a uridine analogue selected by a method comprising
the steps of: providing a uridine analogue unsubstituted in the
5-position; testing said uridine analog for activation by
thymidylate synthase; and selecting said uridine analog when found
to be activated by thymidylate synthase; wherein said uridine
analogue is labeled with a positron emitter; and (b) determining an
extent of maximum thymidylate synthase inhibition and persistence
of thymidylate synthase inhibition over time between doses by
external imaging.
47. A method for assessing the response of tumors to treatment with
a combination of thymidylate synthase inhibitor and at least one
additional compound with antitumor activity, comprising the steps
of: (a) administering a combination of a uridine analogue and at
least one additional compound with anti-tumor activity, wherein
said uridine analogue is selected by a method comprising the steps
of: providing a uridine analogue unsubstituted in the 5-position;
testing said uridine analog for activation by thymidylate synthase;
and selecting said uridine analog when found to be activated by
thymidylate synthase; wherein said uridine analogue is labeled with
a positron emitter; and (b) determining an extent of maximum
thymidylate synthase inhibition and persistence of thymidylate
synthase inhibition over time between doses by external
imaging.
48. The method of claim 47, wherein said at least one additional
compound with anti- tumor activity comprises a uridine analog.
49. A compound of the formula: 9wherein: A=N, C; B=H, hydroxyl,
halogen, acyl (C.sub.1-C.sub.6), alkyl, alkoxy (C.sub.1-C.sub.6);
D=O, S, NH.sub.2; E=H, alkyl, substituted alkyl, alkenyl,
substituted alkenyl, alkoxy, substituted alkoxy, halogen, or any
substituent which is readily cleaved in the body to generate H,
alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkoxy,
substituted alkoxy, or halogen; at least one of W, X, Y, Z is a
label or a label containing moiety having sufficient isotopic
activity for imaging and the remainder of W, X, Y, Z=H, hydroxyl,
halogen, alkyl (Cl-C.sub.6), substituted alkyl (Cl-C.sub.6), alkoxy
(Cl-C.sub.6), substituted alkoxy (C.sub.1-C.sub.6); J=C, S; and
K=O, C.
50. A compound according to claim 49, wherein E is selected from H,
methyl and iodine.
51. A method of diagnosing tumors which are resistant to
thymidylate synthase inhibitors, comprising the steps of: (a)
administering a uridine analogue selected by a method comprising
providing a uridine analogue unsubstituted in the 5-position;
testing said uridine analog for activation by thymidylate synthase;
and selecting said uridine analog when found to be activated by
thymidylate synthase prior to obtaining biopsy specimens; (b)
obtaining biopsy specimens; and (c) analyzing DNA from the biopsy
specimens for extent of analogue incorporation.
52. A method of diagnosing tumors which are resistant to
thymidylate synthase inhibitors, comprising the steps of: (a)
administering to said tumors a uridine analogue labeled with a
positron emitting isotope selected by a method comprising providing
a uridine analogue unsubstituted in the 5-position; testing said
uridine analog for activation by thymidylate synthase; and
selecting said uridine analog when found to be activated by
thymidylate synthase; and (b) analyzing DNA incorporation in said
tumor by external imaging.
53. A method of treating cancer, comprising: administering a
uridine analog in an amount effective to inhibit the replication or
spread of cancer cells, said uridine analog selected by a method
comprising the steps of: providing a uridine analogue unsubstituted
in the 5-position; testing said uridine analog for activation by
thymidylate synthase; and selecting said uridine analog when found
to be activated by thymidylate synthase.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of U.S. provisional
application No. 60/055,525, filed Aug. 8, 1997.
TECHNICAL FIELD
[0002] The present invention relates to the field of drug discovery
and specifically, the design of prodrugs which are substrates for
an intracellular enzyme critical to resistance to cancer
therapeutics in pathological cells and converted to a cell toxin by
the intracellular enzyme.
BACKGROUND
[0003] Throughout this disclosure, various publications are
referenced by first author and date, patent number or publication
number. The full bibliographic citation for each reference can be
found at the end of this application, immediately preceding the
claims. The disclosures of these references are hereby incorporated
by reference into this disclosure to more fully describe the state
of the art to which this invention pertains.
[0004] Cancer cells are characterized by uncontrolled growth,
de-differentiation and genetic instability. The instability
expresses itself as aberrant chromosome number, chromosome
deletions, rearrangements, loss or duplication beyond the normal
dipoid number. Wilson, J. D. et al. (1991). This genomic
instability may be caused by several factors. One of the best
characterized is the enhanced genomic plasticity which occurs upon
loss of tumor suppression gene function (e.g., Almasan A. et al.
(1995)). The genomic plasticity lends itself to adaptability of
tumor cells to their changing environment, and may allow for the
more frequent mutation, amplification of genes, and the formation
of extrachromosomal elements (Smith, K. A. et al. (1995) and
Wilson, J. D. et al. (1991)). These characteristics provide for
mechanisms resulting in more aggressive malignancy because it
allows the tumors to rapidly develop resistance to natural host
defense mechanisms, biologic therapies (Wilson, J. D. et al. (1991)
and Shepard, H. M. et al. (1988)), as well as to chemotherapeutics.
Almasan, A. et al. (1995) and Wilson, J. D. et al. (1991).
[0005] Cancer is one of the most commonly fatal human diseases
worldwide. Treatment with anticancer drugs is an option of steadily
increasing importance, especially for systematic malignancies or
for metastatic cancers which have passed the state of surgical
curability. Unfortunately, the subset of human cancer types that
are amenable to curative treatment today is still rather small
(Haskell, C. M. eds. (1995), p. 32). Progress in the development of
drugs that can cure human cancer is slow. The heterogeneity of
malignant tumors with respect to their genetics, biology and
biochemistry as well as primary or treatment-induced resistance to
therapy mitigate against curative treatment. Moreover, many
anticancer drugs display only a low degree of selectivity, causing
often severe or even life threatening toxic side effects, thus
preventing the application of doses high enough to kill all cancer
cells. Searching for anti-neoplastic agents with improved
selectivity to treatment-resistant pathological, malignant cells
remains therefore a central task for drug development. In addition,
widespread resistance to antibiotics is becoming an important,
world-wide, health issue. Segovia, M. (1994) and Snydman, D. R. et
al. (1996).
[0006] Classes of Chemotherapeutic Agents
[0007] The major classes of agents include the alkylating agents,
antitumor antibiotics, plant alkaloids, antimetabolites, hormonal
agonists and antagonists, and a variety of miscellaneous agents.
See Haskell, C. M., ed., (1995) and Dorr, R. T. and Von Hoff, D.
D., eds. (1994).
[0008] The classic alkylating agents are highly reactive compounds
that have the ability to substitute alkyl groups for the hydrogen
atoms of certain organic compounds. Alkylation of nucleic acids,
primarily DNA, is the critical cytotoxic action for most of these
compounds. The damage they cause interferes with DNA replication
and RNA transcription. The classic alkylating agents include
mechlorethamine, chlorambucil, melphalan, cyclophosphamide,
ifosfamide, thiotepa and busulfan. A number of nonclassic
alkylating agents also damage DNA and proteins, but through diverse
and complex mechanisms, such as methylation or chloroethylation,
that differ from the classic allylators. The nonclassic alkylating
agents include dacarbazine, carmustine, lomustine, cisplatin,
carboplatin, procarbazine and altretamine.
[0009] The clinically useful antitumor drugs are natural products
of various strains of the soil fungus Streptomyces. They produce
their tumoricidal effects by one or more mechanisms. All of the
antibiotics are capable of binding DNA, usually by intercalation,
with subsequent unwinding of the helix. This distortion impairs the
ability of the DNA to serve as a template for DNA synthesis, RNA
synthesis, or both. These drugs may also damage DNA by the
formation of free radicals and the chelation of important metal
ions. They may also act as inhibitors of topoisomerase II, an
enzyme critical to cell division. Drugs of this class include
doxorubicin (Adriamycin), daunorubicin, idarubicin, mitoxantrone,
bleomycin, dactinomycin, mitomycin C, plicamycin and
streptozocin.
[0010] Plants have provided some of the most useful antineoplastic
agents. Three groups of agents from this class are the Vinca
alkaloids (vincristine and vinblastine), the epipodophyllotoxins
(etoposide and teniposide) and paclitaxel (Taxol). The Vinca
alkaloids bind to mictotubular proteins found in dividing cells and
the nervous system. This binding alters the dynamics of tubulin
addition and loss at the ends of mitotic spindles, resulting
ultimately in mitotic arrest. Similar proteins make up an important
part of nervous tissue; therefore, these agents are neurotoxic. The
epipodophyllotoxins inhibit topoisomerase II and therefore have
profound effects on cell function. Paclitaxel has complex effects
on microtubules.
[0011] The antimetabolites are structural analogs of normal
metabolites that are required for cell function and replication.
They typically work by interacting with cellular enzymes. Among the
many antimetabolites that have been developed and clinically tested
are methotrexate, 5-fluorouracil (5-FU), floxuridine (FUDR),
cytarubine, 6-mercaptopurine (6-MP), 6-thioguanine,
deoxycoformycin, fludarabine, 2-chlorodeoxyadenosine, and
hydroxyurea.
[0012] Endocrine manipulation is an effective therapy for several
forms of neoplastic disease. A wide variety of hormones and hormone
antagonists have been developed for potential use in oncology.
Examples of available hormonal agents are diethylstilbestrol,
tamoxifen, megestrol acetate, dexamethasone, prednisone,
aminoglutethimide, leuprolide, goserelin, flutamide, and octreotide
acetate.
[0013] Drawbacks of Current Chemotherapeutic Agents
[0014] Among the problems currently associated with the use of
chemotherapeutic agents to treat cancers are the high doses of
agent required; toxicity toward normal cells, i.e., lack of
selectivity; immunosuppression; second malignancies; and drug
resistance.
[0015] The majority of the agents that are now used in cancer
chemotherapy act by an anti-proliferative mechanism. However, most
human solid cancers do not have a high proportion of cells that are
rapidly proliferating and they are therefore not particularly
sensitive to this class of agent. Moreover, most antineoplastic
agents have steep dose-response curves. Because of host toxicity,
treatment has to be discontinued at dose levels that are well below
the dose that would be required to kill all viable tumor cells.
[0016] Another side effect associated with present day therapies is
the toxic effect of the chemotherapeutic on the normal host tissues
that are the most rapidly dividing, such as the bone marrow, gut
mucosa and cells of the lymphoid system. The agents also exert a
variety of other adverse effects, including neurotoxicity; negative
effects on sexuality and gonadal function; and cardiac, pulmonary,
pancreatic and hepatic toxicities; vascular and hypersensitivity
actions, and dermatological reactions.
[0017] Hematologic toxicity is the most dangerous form of toxicity
for many of the antineoplastic drugs used in clinical practice. Its
most common form is neutropenia, with an attendant high risk of
infection, although thrombocytopenia and bleeding may also occur
and be life threatening. Chemotherapy may also induce qualitative
defects in the function of both polymorphonuclear leukocytes and
platelets. The hematopoieic growth factors have been developed to
address these important side effects. Wilson, J. D. et al. (1991)
and Dorr, R. T. and Von Hoff D. D., eds. (1994).
[0018] Most of the commonly used antineoplastic agents are capable
of suppressing both cellular and humoral immunity. Infections
commonly lead to the death of patients with advanced cancer, and
impaired immunity may contribute to such deaths. Chronic, delayed
immunosuppression may also result from cancer chemotherapy.
[0019] The major forms of neurotoxicity are arachnoiditis;
myelopathy or encephalomyelopathy; chronic encephalopathies and the
somnolence syndrome; acute encephalopathies; peripheral
neuropathies; and acute cerebellar syndromes or ataxia.
[0020] Many of the commonly employed antineoplastc agents are
mutagenic as well as teratogenic. Some, including procarbazine and
the alkylating agents, are clearly carcinogenic. This carcinogenic
potential is primarily seen as delayed acute leukemia in patients
treated with polyfunctional alkylating agents and inhibitors of
topoisomerase II, such as etoposide and the anthracycline
antibiotics. Chemotherapy has also been associated with cases of
delayed non-Hodgkin's lymphoma and solid tumors. The present
invention will minimize these effects since the prodrug will only
be activated within tumor cells.
[0021] The clinical usefulness of a chemotherapeutic agent may be
severely limited by the emergence of malignant cells resistant to
that drug. A number of cellular mechanisms are probably involved in
drug resistance, e.g., altered metabolism of the drugs,
impermeability of the cell to the active compound or accelerated
drug elimination from the cell, altered specificity of an inhibited
enzyme, increased production of a target molecule, increased repair
of cytotoxic lesions, or the bypassing of an inhibited reaction by
alternative biochemical pathways. In some cases, resistance to one
drug may confer resistance to other, biochemically distinct drugs.
Amplification of certain genes is involved in resistance to
biologic and chemotherapy. Amplification of the gene encoding
dihydrofolate reductase is related to resistance to methotrexate,
while amplification of the gene encoding thymidylate synthase is
related to resistance to treatment with 5-fluoropyrimidines. Table
1 summarizes some prominent enzymes in resistance to biologic and
chemotherapy.
1TABLE 1 Enzymes Overexpressed in Resistance to Chemotherapy
Biologic or Enzyme Chemotherapy Referenced (Examples) Thymidylate
Uracil-based Lonn, U. et al. synthase Folate-based Kobayashi, H. et
al. Quinazoline-based Jackman, AL et al. Dihydrofolate Folate-based
Banerjee, D. et al. reductase Bertino, J. R. et al. Tyrosine
kinases TNF-alpha Hudziak, R. M. et al. Multidrug Stuhlinger, M. et
al. resistance MDR-associated Multidrug Simon, S. M. and Schindler,
proteins (ABC P-gp resistance M. Gottesman, M. M. et al. proteins)
CAD* PALLA** Smith, K. A. et al. Dorr, R. T. and Von Hoff, D. D.,
eds. Ribonucleotide Hydroxyurea Wettergren, Y. et al. reductase
Yen, Y. et al. *CAD = carbamyl-P synthase, aspartate
transcarbamylase, dihydrocrotase **PALA =
N-(phosphonacetyl)-L-aspartate
[0022] Use of Prodrugs as a Solution to Enhance Selectivity of a
Chemotherapy Agent
[0023] The poor selectivity of anticancer agents has been
recognized for a long time and attempts to improve selectivity and
allow greater doses to be administered have been numerous. One
approach has been the development of prodrugs. Prodrugs are
compounds that are toxicologically inert but which may be converted
in vivo to active toxic products. In some cases, the activation
occurs through the action of a non-endogenous enzymes delivered to
the target cell by antibody ("ADEPT" or antibody-dependent enzyme
prodrug therapy (U.S. Pat. No. 4,975,278)) or gene targeting
("GDEPT" or gene dependent enzyme-prodrug therapy (Melton, R. G.
and Sherwood, R. F. (1996)). These technologies have severe
limitations with respect to their ability to exit the blood and
penetrate tumors. Connors, T. A. and Knox, R. J. (1995).
[0024] Accordingly, there is a need for more selective agents which
can penetrate the tumor and inhibit the proliferation and/or kill
cancer cells that have developed resistance to therapy. The present
invention satisfies this need and provides related advantages as
well.
SUMMARY OF THE INVENTION
[0025] This invention provides a method for identifying therapeutic
agents by contacting a target or test cell with a candidate
therapeutic agent or prodrug which is a selective substrate for a
target enzyme in the cell. In one embodiment, the target enzyme is
an endogenous, intracellular enzyme which is overexposed and
confers resistance to biologic and chemotherapeutic agents. In a
separate embodiment, the activity of the enzyme has been greatly
enhanced in a tumor cell as a result of loss of tumor suppressor
function (Smith, K. A. et al. (1995) and Li, W. et al. (1995))
and/or selection resulting from previous exposure to chemotherapy,
(Melton, R. G. and Sherwood, R. F. (1996)). In a separate
embodiment, the target enzyme is an expression product of a foreign
gene in the cell, wherein the foreign gene encodes a target
enzyme.
[0026] After the cell is contacted in vitro and/or in vivo with the
candidate prodrug, the cell is assayed for efficacy of the agent by
noting if the agent caused a reduction in cellular proliferation or
if the agent kills the cell. In one aspect of this invention, the
prodrug kills the cell or inhibits the cellular proliferation by
the release of a toxic byproduct from the prodrug by the target
enzyme. In a further aspect of this invention, one or more "target
enzymes" can be used to activate the prodrug so that it releases
the toxic byproduct.
[0027] Another aspect of this invention includes kits for use in
assaying for new prodrugs having the characteristics described
herein against target enzymes. The kits comprise the reagents and
instructions necessary to complete the assay and analyze the
results.
[0028] This invention also provides methods and examples of
molecules for selectively killing a pathological cell by contacting
the cell with a prodrug that is a selective substrate for a target
enzyme, e.g., an endogenous, intracellular enzyme as defined above.
The substrate is specifically converted to a cellular toxin by the
intracellular target enzyme. In another aspect of this invention,
the product of an initial prepatory reaction is subsequently
activated by a common cellular enzyme such as an acylase,
phosphatase or other "housekeeping" enzyme. Voet, et al. (1995) to
release the toxic byproduct from the prodrug.
[0029] Further provided by this invention is a method for treating
a pathology characterized by pathological, hyperproliferative cells
in a subject by administering to the subject a prodrug that is a
selective substrate for a target enzyme, and selectively converted
by the enzyme to a cellular toxin in the hyperproliferative cell.
The prodrugs of this invention may be used alone or in combination
with other chemotherapeutics or alternative anticancer therapies
such as radiation.
[0030] A further aspect of this invention is the preparation of a
medicament for use in treating a pathology characterized by
pathological, hyperproliferative cells in a subject by
administering to the subject a prodrug that is a selective
substrate for a target enzyme, and selectively converted by the
enzyme to a cellular toxin in the hyperproliferative cell.
BRIEF DESCRIPTION OF THE FIGURES
[0031] FIG. 1 shows the development of resistance to anti-cancer
modalities in cells, and the consequences.
[0032] FIG. 2 schematically shows activation pathways of the
prodrugs of this invention.
[0033] FIG. 3 schematically shows the High Throughput Screen for
prodrugs activated by intracellular enzymes important in drug
resistance.
[0034] FIG. 4 schematically shows how lead human thymidylate
synthase (TS) prodrugs are assayed using TS-negative E. coli as the
cell target.
[0035] FIG. 5 shows an example of how to use this screen to
simultaneously optimize the prodrug for reactivity to two target
enzymes.
DETAILED DESCRIPTION OF THE INVENTION
[0036] The invention is achieved by exploiting some of the key
genomic and phenotypic changes intimately linked to resistance to
biologic and chemotherapy of cancer cells. The invention provides a
means for in vivo selectively inhibiting the growth and/or killing
of cells which have undergone selection by exposure to cancer
therapy (including biologic therapy such as tumor necrosis factor
(TNF) or chemotherapy). (Refer to Table 1). As a result, certain
enzymes which have been activated by mutation or gene amplification
are resistant to further therapy by the agent. Unlike prior art
therapies directed to creating more potent inhibitors of
endogenous, intracellular enzymes, this invention exploits the
higher enzyme activity associated with therapy-resistant diseased
cells and tissues versus normal cells and tissues and does not rely
on inhibiting the enzyme. In one aspect, the tumor cells
successfully treated by the prodrugs of this invention are
characterized by enhanced target enzyme activity and therefore have
a much higher potential to convert the prodrug to its toxic form
than do normal cells which do not overexpress the target enzyme.
The term "target enzyme" is used herein to define enzymes having
one or more of the above noted characteristics.
[0037] As used herein, the terms "host cells, "target cells" and
"hyperproliferative cells" encompass cells characterized by the
activation by genetic mutation or the endogenous overexpression of
an intracellular enzyme. In some embodiments, the overexpression of
the enzymes is related to drug resistance or the genetic
instability associated with a pathological phenotype. A number of
cellular mechanisms are involved in drug resistance, e.g., altered
metabolism of the drug, impermeability of the cell with regard to
the active compound or accelerated drug elimination from the cell,
altered specificity of an inhibited enzyme, increased production of
a target molecule, increased repair of cytotoxic lesions, or the
bypassing of an inhibited reaction by alterative biochemical
pathways. Enzymes activated or overexpressed an related to drug
resistance include, but are not limited to thymidylate synthase
(TS) (Lonn, U. et al. (1996); Kobayashi, H. et al. (1995); Jackman,
A. L. et al. (1995)), dihydrofolate reductase (Banerjee, D. et al.
(1995) and Bertino, J. R. et al. (1996)), tyrosine kinases
(TNF-.alpha., Hudziak, R. M. et al. (1988)) and multidrug
resistance (Stuhlinger, M. et al. (1994)); Akdas, A. et al. (1996);
and (Tannock, I. F. (1996)); and ATP-dependent multidrug resistance
associated proteins (Simon, S. M. and Schindler, M. (1994)).
Alternatively, resistance to one drug may confer resistance to
other, biochemically distinct drugs. While this application is
specifically directed to cancer, a similar approach can be applied
to enzymes encoded by human and animal pathogens, and in which the
inhibitors have failed due to development of resistance.
[0038] Amplification of certain genes is involved in resistance to
chemotherapy. Amplification of dihydrofolate reductase (DHFR) is
related to resistance to methotrexate while amplification of the
gene encoding thymidylate synthase is related to resistance to
tumor treatment with 5-fluoropyrimidnes. Amplification of genes
associated with drug resistance can be detected and monitored by a
modified polymerase chain reaction (PCR) as described in
Kashini-Sabet, et al. (1988) or U.S. Pat. No. 5,085,983. Acquired
drug resistance can be monitored by the detection of cytogenetic
abnormalities, such as homogeneous chromosome staining regions and
double minute chromosomes both of which are associated with gene
amplification. Alternative assays include direct or indirect enzyme
activity assays and both of which are associated with gene
amplification (e.g., Carreras & Santi (1995)); other
methodologies (e.g. polymerase chain reaction, Houze, T. A. et al.
(1997) or immunohistochemistry (Johnson, P. G. et al. (1997)).
[0039] Alternatively, the target cell is characterized as having
inactivated tumor suppressor function, e.g. loss or inactivation of
retinoblastoma (RB) or p53, known to enhance expression of TS (Li,
W. et al. (1995)) or DHFR (Berino, et al. (1996) and Li, W. et al.
(1995)).
[0040] The prodrugs of this invention are useful to treat or
ameliorate any disease wherein the disease-associated enzyme is
associated with drug resistance to a chemotherapeutic and in some
embodiments, where the enzyme is overexpressed over-accumulated or
activated in pathological cells versus normal cells, for example,
the TS enzyme. Particularly excluded is the enzyme
glutathione-S-transferase which has been shown to be elevated in
some human tumors. Morgan, A. S. et al. (1998). The prodrugs of the
subject invention are distinguishable on the basis that the target
enzymes of this invention are commonly overexpressed,
overaccumulated or activated in pathological cells versus normal
cells. The most important principle which distinguishes the current
invention from other approaches are:
[0041] (1) This invention describes the synthesis of substrates for
enzymes like thymidylate synthase. The overexpressed enzyme will
generate toxin, preferentially in diseased cells. Previous
approaches have relied on inhibitor. The inhibitors lead to
amplified expression of the enzyme, and subsequent resistance to
treatment (see, e.g., Lonn, U. et al. (1996).
[0042] (2) The current approach is also distinguishable from other
"substrate-prodrug" approaches, e.g., the glutathione-S-transferase
enzymes (see, e.g., Morgan, A. S. et al. (1998). The enzymes of the
GST family are expressed at increased levels in response to toxic
insult to the cell. The GST family of enzymes have overlapping
substrate specificities, which makes it impossible to design a
substrate reactive with only a single species of enzyme with
elevated expression in a cancer cell (Morgan, A. S. et al. (1998)).
Because each of the enzymes of the current invention (e.g.,
thymidylate synthase, dihydrofolate reductase and thymidyline
kinase) is unique with respect to its structure and substrate
specificity, it is facile to design unique substrates. Several
examples of substrates for thymidylate synthase are provided in the
specifications of this application.
[0043] (3) In some cases the gene encoding the target enzyme (e.g.,
thymidylate synthase) may have undergone mutation to give
resistance to inhibitors, but will still be capable of carrying out
reaction with non-inhibitor substrates. Barbour, K. W. et al.
(1992) and Dicken, A. P. et al. (1993).
[0044] Drug Assay
[0045] This invention provides a method for identifying agents
which have therapeutic potential for the treatment of
hyproliferative or neoplastic disorders, e.g., cancer. The method
also identifies agents that inhibit the growth of cells or cell
cycling of hyperproliferative cells, such as cancer cells. Other
cells that are included are bacterial, yeast and parasitic cells
which cause disease as a result of inappropriate proliferation in
the patient. The agent is considered a potential therapeutic agent
if cell proliferation, replication or cell cycling is reduced
relative to the cells in a control sample. Most preferably, the
cells are killed by the agent. The cells can be procaryotic
(bacterial such as E. coli) or eucaryotic. The cells can be
mammalian or non-mammalian cells, e.g., mouse cells, rat cells,
human cells, fungi (e.g., yeast) or parasites (e.g., Pheumocysti or
Leishmania) which cause disease.
[0046] As used herein, a "hyperproliferative cell" is intended to
include cells that are de-differentiated, immortalized neoplastic,
malignant, metastatic or transformed. Examples of such cells
include, but are not limited to a sarcoma cell a leukemia cell, a
carcinoma cell, or an adenocarcinoma cell. More specifically, the
cell can be a breast cancer cell, a hepatoma cell, a colorectal
cancer cell, pancreatic carcinoma cell, an oesophageal carcinoma
cell, a bladder cancer cell, an ovarian cancer cell, a skin cancer
cell, a liver carcinoma cell, or a gastric cancer cell. In an
alternative embodiment, the target cell can be resistant to a drug
or compound used to prevent or kill a cell infected with an
infectious agent which is resistant to conventional antibiotics.
Infectious agents include bacteria, yeast and parasites, such as
trypanosomes.
[0047] Specific examples of target enzymes that are the subject
matter of this invention are listed in Table 1 (above) or Table 2
(below). These enzymes are involved in resistance to chemotherapy,
are endogeneously activated, overexpressed or over-accumulated in a
cell characterized by resistance to cancer therapy and associated
with a pathological or disease include, but are not limited to
enzymes such as a member of the tyrosine kinase superfamily or an
ATP dependent MDR-associated protein, CAD, thymidylate synthase,
dihydrofolate reductase, and ribonucleotide reductase. Table 2
provides a list of enzymes which may be targeted by this approach
in infectious disese.
2TABLE 2 Enzymes Overexpressed in infectious disease, and which
contribute to drug resistance Enzyme Provides increased Resistance
to: Beta-lactamases Penicillin and other beta-lactam containing
antibiotics Aminoglycosidase, or Aminoglycoside antibiotics
aminoglycoside midifying enzymes (e.g., streptomycin, gentamycin)
Chloramphenicol transacetylase Chloramphenicol Trimethoprim
Dihydrofolate reductase Reference: Mechanisms of Microbial Disease,
2.sup.nd Ed., M. Schaechter, G. Medloff, B. I. Eisenstein, Editor
TS Satterfield. Publ. Williams and Wilkins, pp. 973 (1993).
[0048] The potentially therapeutic agent identified by the method
of this invention is a prodrug that is a substrate for the enzyme
and is converted intracellularly to an intacellular toxin. As used
herein, a "prodrug" is a precursor or derivative form of a
pharmaceutically active agent or substance that is less cytotoxic
to target or hyperproliferative cells as compared to the drug
metabolite and is capable of being enzymatically activated or
converted into the more active form (see Connors, T. A. (1986) and
Connors, T. A. (1996)). The toxicity of the agent is directed to
cells that are producing the converting enzyme in an amount
effective to produce a therapeutic concentration of the cellular
toxin in the diseased cell.
[0049] This invention also provides a quick and simple assay that
will enable initial identification of compounds with at least some
of the desired characteristics. For purposes of this current
invention, the general scheme of one embodiment is shown in FIG. 3.
This drawing describes how the assay is arranged and the materials
necessary for its process. As show in FIG. 3, the assay requires
two cell types, the first being a control cell in which the target
enzyme is not expressed, or is expressed at a low level. The second
cell type is the test cell, in which the target enzyme is expressed
at a detectable level e.g., a high level. For example, a
procaryotic E. coli which does not endogenously express the target
enzyme TS is a suitable host cell or target cell. The cell can have
a control counterpart (lacking the target enzyme), or in a separate
embodiment, a counterpart genetically modified to differentially
express the target enzyme, or enzymes (containing the appropriate
species of target enzyme). More than one species of enzyme can be
used to separately transduce separate host cells, so that the
effect of the candidate drug on a target enzyme can be
simultaneously compared to its effect on another enzyme or a
corresponding enzyme from another species.
[0050] In another embodiment, transformed cell lines, such as
ras-transformed NIH 3T3 cells (ATCC, 10801 University Blvd.,
Manassas, Va. 20110-2209, U.S.A.) are engineered to express
variable and increasing quantities of the target enzyme of interest
from cloned cDNA coding for the enzyme. Transfection is either
transient or permanent using procedures well known in the art and
described in Chen, L. et al. (1996), Hudziak, R. M. et al. (1988),
or Carter, P. et al. (1992). Suitable vectors for insertion of the
cDNA are commercially available from Stratagene, La Jolla, Calif.
and other vendors. The level of expression of enzyme in each
transfected cell line can be monitored by immunoblot and enzyme
assay in cell lysates, using monoclonal or polyclonal antibody
previously raised against the enzyme for immunodetection. See,
e.g., as described by Chen, L. et al. (1996). The amount of
expression can be regulated by the number of copies of the
expression cassette introduced into the cell or by varying promoter
usage. Enzymatic assays also can be performed as reviewed by
Carreras, C. W. and Santi, D. V. (1995).
[0051] As noted above, cells containing the desired genetic
deficiencies may be obtained from Cold Spring Harbor, the
Agricultural Research Service Culture Collection, or the American
Type Culture Collection. The appropriate stains can also be
prepared by inserting into the cell a gene coding for the target
enzyme using standard techniques as described in Miller (1992),
Sanbrook, et al. (1989), and Spector, et al. (1997). Growth assays
can be performed by standard methods as described by Miller (1992)
and Spector, et al. (1997).
[0052] It should be understood by those skilled in the art that the
screen shown in FIG. 3 can be applied broadly for the discovery of
antibiotics. For example, thymidylate synthase from yeast could be
substituted for that of E. coli in FIG. 4. This would allow the
discovery of specific antifungal antibiotics targeting yeast
related pathogens. In addition, other enzymes can be subjected to
this. For example, prodrugs which target specifically the
dihydrofolate reductase activity of infectious agents, like
Pneumocystis carnii, could be selected. These agents will be
selected for specificity for the target enzyme, and can be shown
not to activate the enzyme of the natural host by employing the
screening assay described in FIG. 3. The control cellular
constructs would contain the corresponding normal human enzyme, in
order to show lack of toxicity when only the normal human enzyme is
present.
[0053] For example and as shown in FIG. 4, a foreign gene, e.g., a
human gene encoding TS, can be inserted into the host cell such
that human TS is expressed. This genetically engineered cell is
shown as the "test cell" in FIG. 3. The "control cell" does not
express the target enzyme. In some embodiments it may be necessary
to supplement the culture media with the protein product of the
target enzyme.
[0054] In a separate embodiment, the wild type host cell is
deficient or does not express more than one enzyme of interest. As
shown in FIG. 4, the host cell does not endogenously produce
thymidine kinase (TK.sup.-) or thymidylate synthase (TS.sup.-).
Genes coding for the human counterpart of these enzymes are
introduced into the host cell to obtain the desired level of
expression. The level of expression of enzyme in each transfected
cell line can be monitored by methods described herein, e.g., by
immunoblot and enzyme assay in cell lysates, using monoclonal or
polyclonal antibody previously raised against the enzyme for
immunodetection. See, e.g., as described by Chen, L. et al. (1996).
Enzymatic assays also can be performed as reviewed by Carerras, C.
W. and Santi, D. N. (1995) using detectably labeled subsituents,
e.g. tritium labeled substitutes.
[0055] The test cell is grown in small multi-well plates and is
used to detect the biologic activity of test prodrugs. For the
purposes of this invention, the successful candidate drug will
block the growth or kill the test cell type, but leave the control
cell type unharmed.
[0056] The candidate prodrug can be directly added to the cell
culture media or previously conjugated to a ligand specific to a
cell surface receptor and then added to the media. Methods of
conjugation for cell specific delivery are well known in the art,
see e.g., U.S. Pat. Nos. 5,459,127; 5,264,618; and published patent
specification WO 91/17424 (published Nov. 14, 1991). The leaving
group of the candidate prodrug can be detectably labeled, e.g.,
with tritium. The target cell or the culture media is then assayed
for the amount of label released from the candidate prodrug.
Alternatively, cellular uptake may be enhanced by packaging the
prodrug into liposomes using the method described in Lasic, D. D.
(1996) or combined with cytofectin as described in Lewis, J. G. et
al. (1996).
[0057] In a separate embodiment, cultured human tumor cells
overexpressing the enzyme of interest i.e., target enzyme, are
identified as described above. The cells are contacted with the
potential therapeutic agent under conditions which favor the
incorporation of the agent into the intracellular compartment of
the cell. The cells are then assayed for inhibition of cellular
proliferation or cell killing.
[0058] Provided below is a brief summary of cells and target
enzymes that are useful to activate the prodrugs of this
invention.
[0059] Thymidylate Synthase
[0060] The overexpression of thymidylate synthase is associated
with colon cancer, breast cancer, gastric cancer, head and neck
cancer, liver cancer and pancreatic cancer. These diseases are
currently treated by antimetabolite drugs (uracil-based,
folate-based, or quinaszoline-based (see Table 1)). In each of
these cases it is likely that the 5-fluorouracil therapy can lead
to amplified activity of TS, or select for drug resistant forms of
the enzyme, and thereby lead to drug-resistance of the disease
relapse. Lonn, U. et al. (1996) reported that amplification of the
TS gene occurred in breast cancer patients who previously received
adjuvant chemotherapy (cyclophosphamide, methotrexate,
5-fluomuracil [CMF]) after surgery. The principal reaction normally
performed by TS is the synthesis of deoxythymidine monophosphate
(dTMP) and dihydrofolate (DH) from deoxyuridine monophosphate
(dUMP) and N(5),N(10)methylene-tetrahydrofolate (THF). In one
embodiment, a derivative of uracil or THF is provided to cells
expressing TS. For purposes of this invention, "uracil" (base only)
and "uridine" (base and sugar) are used interchangeably and
synonymously.
[0061] The derivative or "prodrug" is converted by the enzyme into
highly cytotoxic metabolites. The low level of TS expressed in
normal cells will not produce a toxic amount of the converted
toxin. High levels of TS expressed in disease tissues generate more
toxin and thereby lead to an inhibition of cell proliferation
and/or cell death. For example, current therapy utilizes
5-fluorodeoxyuridylate to inhibit TS activity. During the reaction
with substrate, the fluorine atom irreversibly binds to the TS
enzyme and inhibits it. In contrast to one embodiment of the
present invention, the prodrugs allow TS to complete the reaction
but generates a modified product that, when incorporated into DNA,
canes a toxic effect. The enzyme product may also block other
critical cellular functions (e.g. protein synthesis or energy
metabolism). Conversion of the prodrug also can release a
metabolite, such as Br.sup.- or I.sup.- or CN.sup.- which is toxic
to the cell. Derivatives of uracil/dUMP and N(5)(10)-THF can be
synthesized all of which have the potential of generating toxic
product after metabolically catalyzed by TS.
[0062] Synthesis of 5-substituted pyrimidine nucleosides and
5-substituted pyrimidine nucleoside monophosphats can be
accomplished by methods that are well-known in the art. For
example, treatment of 5-chloromercuri-2'-deoxyuridine with
haloalkyl compounds, hoaces or haloalkenes in the presence of
Li.sub.2PdCl.sub.4 results in the formation, through an
organopalladium intermediate, of the 5-alkyl, 5-acetyl or 5-alkene
derivative, respectively. Wataya, et al. (1979) and Bergstrom, et
al. (1981). Another example of C5-modification of pyrimidine
nucleosides and nucleotides is the formation of C5-trans-styryl
derivatives by treatment of unprotected nucleotide with mercuric
acetate followed by addition of styrene or ring-substituted
styrenes in the presence of Li.sub.2PdCl.sub.4. Bigge, et al.
(1980). Pyrimidine deoxyribonucleoside triphosphates were
derivatize with mercury at the 5 position of the pyridine ring by
treatment with mercuric acetate in acetate buffer at 50.degree. for
3 hours. Dale, et al. (1973). Such treatment would also be expected
to be effective for modification of monophosphates; alteratively, a
modified triphosphate could be converted enzymatically to a
modified monophosphate, for example, by controlled treatment with
alkaline phosphatase followed by purification of monophosphate.
Other moieties, organic or nonorganic, with molecular properties
similar to mercury but with preferred pharmacological properties
could be substituted. For general methods for synthesis of
substituted pyrimidines, for example, U.S. Pat. Nos. 4,247,544;
4,267,171; and 4,948,882; and Bergstom et al. (1981). The above
methods would also be applicable to the synthesis of derivatives of
5-substituted pyrimidine nucleosides and nucleotides containing
sugars other than ribose or 2'-deoxyribose, for example
2'-3'-dideoxyribose, arabinose, furanose, lyxose, pentose, hexose,
heptose, and pyranose. An example of such a subsituents are
halovinyl groups, e.g. E5-(2-bromovinyl)-2'-deoxyu- ridylate. Barr,
F. J. et al. (1983). In this reference the authors demons that the
normally inert substituent at the 5-position (bromovinyl) is
convertible to a chemically reactive group as a result of
enzyme-mediated nucleophilic attack at the 6-position of the
uridine heterocycle, leading to the production of a reactive
alkylating agent. This compound is not useful from the point of
view of the current application because it cannot be activated by
endogenous thymidine kinase, and because its conversion by
thymidylate synthase leads to inactivation of the thymidylate
synthase (Balzarini, et al., 1987). However, improved subsituents
will be synthesized and compared for reactivity with TS and
specific cytotoxicity to TS-overproducing tumor cells.
[0063] Alternatively, 5-bromodeoxyuridine, 5-iododeoxyuridine, and
their monophosphate derivatives are available commercially firm
Glen Research, Stering, Va. (USA), Sigma-Aldrich Corporation, St.
Louis, Mo. (USA), Moravek Biochemicals, Inc., Brea, Calif. (USA),
ICN, Costa Mesa, Calif. (USA) and New England Nuclear, Boston,
Mass. (USA). Commercially-available 5-bromodeoxyuridine and
5-iododeoxyuridine can be converted to their monophosphates either
chemically or enzymatically, though the action of a kinase enzyme
using commercial available reagents from Glen Research, Sterling,
Va. (USA) and ICN, Costa Mesa, Calif. (USA). These halogen
derivatives could be combined with other subsituents to create
novel and more potent antimetabolites.
[0064] Primary sequences show that TS is one of the most highly
conserved enzymes. Perry, K. et al. (1990). Crystal structures of
TS from several procaryotic species, Lactobacillus casei (Hardy, L.
W. et al. (1987); Finer-Moore, J. et al. (1993)) and Escherichia
coli (Perry, K et al. (1990)); an eukaryote Leishmania major
(Knighton, E. R. et al. (1994)); and T4 phage (Finer-Mooze, J. S.
et al., (1994)) have been determined and indicate that tertiary
structure also is very well conserved. The sequence alignment of
the species of TS whose three dimensional structures have been
determined and is shown in Schiffer, C. A. et al. (1995). From
these amino acid sequences, the DNA sequences can be deduced or
isolated using methods well known to those of skill in the art.
Sambrook, et al. (1989). Alternatively, some 29 TS sequences from
different organisms have been cloned and deposited into the DNA
databases as described in Carerras, C. W. and Santi, D. V. (1995).
The sequence of human thymidylate synthase gene, its cloning,
expression and purification is provided in Takeishi, K. et al.
(1985), Davisson, V. J. et al. (1989) and Davisson, V. J. et al.
(1994). Genes encoding the TS protein and containing the necessary
regulatory sequences, are constructed using methods well known to
those of skill in the art. The gene encoding TS is introduced to
target cells by electroporation, transformation or transfection
procedures. Sambrook et al. (1989). Alternatively, the gene is
inserted into an appropriate expression vector by methods well
known in the art, e.g., as described in Carreras, C. W. and Santi,
D. V. (1995), Miller (1992) and Spector et al. (1997). The
expression vector inserts the TS gene into the cells. The cells are
then grown under conditions which favor the expression and
production of TS protein.
[0065] Human gastric cancer cell lines, MKN-74, MKN-45, MKN-28 and
KATO-III can be used in the assay described above to identify
potential therapeutic agents which are selective substrates for TS.
MKN-74 and MKN-45 are established from well and poorly
differentiated adenocarcinomas, respectively. These cell lines and
culture conditions are described in Osmki M. et al. (1997) and
references cited therein. Alternatively, tumor cell lines such as
those described by Copur, S. et al. (1995), which have been
selected by 5-FU to overexpress thymidylate synthase may be
used.
[0066] Quantitation of TS can be performed using epic biochemical
assays that are well known to those with skill in the art. To
quantify the level of TS protein and TS gene expression from human
tumor tissue samples, the methods as reported by Johnston, P. G. et
al. (1991) and Horikoshi, T. et al. (1992) provide sensitive
assays. Alternatively, the PCR method of Lonn, U. et al. (1996) is
used to assay TS gene amplification and identify cells that are
useful in the method of identifying therapeutic agents as described
herein.
[0067] As is apparent to one skilled in the art control cell
culture systems without drug and separately with a reference drug
such as the one exemplified below, also am assayed. A preferred
embodiment of the prodrugs is one which preferentially kills target
cells with about 2-fold and preferably about 3-fold or greater
activity than normal cells. This invention also provides the agents
identified by the methods described herein.
[0068] In another aspect, this invention provides a method for
inhibiting the proliferation of a hyperproliferative cell, by first
conducting the above assay. A prodrug identified by this assay is
contacted with the cell and converted to a toxic metabolite in the
cell by an endogenous intacellular enzyme as described above.
[0069] In one embodiment, the endogenous, intracellular enzyme is
thymidylate synthase and the cell is selected from the group
consisting of colorectal cell, head and neck cancer cell, breast
cancer cell, or a gastric cancer cell.
[0070] In a further aspect, the prodrug contacted with the cell
overexpressing thymidylate synthase is an L- or D compound of the
formulae: 1
[0071] which may be in any of their enantiomeric, diasteriomeric,
or stereoisomeric forms, including, for example, D- or L-forms, and
for example, .alpha.- or .beta.-anomeric forms.
[0072] In the above formulae, R.sub.1 (at the 5-position) is or
contains a leaving group which is a chemical entity that has a
molecular dimension and electrophilicity compatible with extraction
from the pyrimidine ring by thymidylate synthase, and which upon
release from the pyrimidine ring by thymidylate synthase, has the
ability to inhibit the proliferation of the cell or kill the
cell.
[0073] In one embodiment, R.sub.1 is or contains a chemical entity
selected from the group consisting of: --Br, --I, -O-alkyl,
-O-aryl, O-heteroaryl, -S-alkyl, -S-aryl, -S-heteroaryl, --CN,
--OCN, --SCN, --NH.sub.2, -NH-alkyl, -N(alkyl).sub.2, --NHCHO,
--NHOH, -NHO-alkyl, NH.sub.2CONHO--, NHNH.sub.2, and --N.sub.3.
Another example of R.sub.1 is derived from cis-platin: 2
[0074] In the above formulae for the L- or D-compound(s), Q is a
chemical entity selected from the group consisting of sugar groups,
thio-sugar groups, carbocyclic groups, and derivatives thereof.
Examples of sugar groups include, but are not limited to,
monosaccharide cyclic sugar groups such as those derived from
oxetanes (4-membered ring sugars), furanoses (5-membered ring
sugars), and pyranoses (6-membered ring sugars). Examples of
furanosyl include threo-furanosyl (from threose, a four-carbon
sugar); erythro-furanosyl (from erythrose, a four-carbon sugar);
ribo-furanosyl (from ribose, a five-carbon sugar); ara-furanosyl
(also often referred to as arabino-furanosyl; from arabinose, a
five-carbon sugar); xylo-furanosyl (from xylose, a five-carbon
sugar); and lyxo-furanosyl (from lyxose, a five-carbon sugar).
Examples of sugar group derivatives include "deoxy", "keto", and
"dethydro" derivatives as well as substituted derivatives. Examples
of thio sugar groups include the sulfur analogs of the above sugar
groups, in which the ring oxygen has been replaced with a sulfur
atom. Examples of carbocyclic groups include C.sub.4 carbocyclic
groups, C.sub.5 carbocyclic groups, and C.sub.6 carbocyclic groups
which may further have one or more subsituents, such as --OH
groups.
[0075] In one embodiment, Q is a furanosyl group of the formula:
3
[0076] wherein R.sub.2 and R.sub.3 arc the same or different and
are independently H or --OH. In one embodiment, R.sub.2 and R.sub.3
are H. In one embodiment, R.sub.2 is OH and R.sub.3 is H. In one
embodiment, R.sub.2 is H and R.sub.3 is OH. In one embodiment,
where R.sub.2 and R.sub.3 are OH.
[0077] In one embodiment, Q is a .beta.-D-ribofuranosyl group of
the formula: 4
[0078] wherein R.sub.2 and R.sub.3 are the same or different and
are independently H or --OH.
[0079] In some embodiments the hydroxymethyl group (for example,
the 4'-hydroxymethyl group of .beta.-D-ribofuranosyl) can be
phosphorylated.
[0080] Modifications of current alkylating agents attached at the
pyrimidine 5-position, and which fit the steric restrictions as
described above can be employed (Haskell, C. M. eds. (1995), pp.
55-58). Cell-free, or cell based, screening assays for release of
constituent at the 5-position of uracil are described by Roberts,
D. (1966) and Hasimoto, Y. et al. (1987).
[0081] In the case where R.sub.1 comprises CN.sup.-, the highly
toxic CN.sup.- moiety is the therapeutically active species.
Because of the highly nonspecific toxic nature of CN.sup.-, it
cannot normally be used in a therapeutic mode. This problem is
overcome by delivering the toxin in the form of a prodrug that will
be significantly activated only in cells which overexpress
thymidylate synthase.
[0082] In addition, a prodrug can be converted to a toxic
metabolite by the intracellular enzyme which, in some embodiments,
can be further modified by an intracellular "housekeeping" enzyme.
An example is shown below. 5
[0083] Description of the "partial" reaction of dUMP and TS, as
well as relevant assays are described in Garett, C. et al. (1979).
Assays for other product, i.e. where a reaction complete product is
an anti-metabolite of the bromovinyl-derivatives of dUNP, are
described by Barr, P. J., et al. (1983). Salts of the prodrug of
the present invention may be derived from inorganic or organic
acids and bases. Examples of acids include hydrochloric,
hydrobromic, sulfuric, nitric, perchloric, fumaric, maleic,
phosphoric, glycollic, lactic, salicyclic, succinic,
toluene-p-sulfonic, tartaric, acetic, citric, methanesulfonic,
ethanesulfonic, formic, benzoic, malonic, naphthalene-2-sulfonic
and benzenesulfonic acids. Other acids, such as oxalic, while not
in themselves pharmaceutically acceptable, can be employed in the
preparation of salts useful as intermediates in obtaining the
compounds of the invention and their pharmaceutically acceptable
acid addition salts. Examples of bases include alkali metal (e.g.,
sodium) hydroxides, alkaline earth metal (e.g., magnesium)
hydroxides, ammonia, and compounds of formula NW.sub.4.sup.+,
wherein W is C.sub.1-4 alkyl.
[0084] Examples of salts include; acetate, adipate, alginate,
aspartate, benzoate, benzenesulfonate, bisulfate, butyrate,
citrate, camphorate, camposulfonate, cyclopentanepropionate,
digluconate, dodecylsulfate, ethanesulfonate, fumarate,
flucoheptanoate, glycerophosphate, hemisulfate, heptanoate,
hexanoate, hydrochloride, hydrobromide, hydroiodide,
2-hydroxyethanesulfonate, lactate, malcate, methanesulfonate,
2-naphthalenesulfonate, nicotinate, oxalate, palmoate, pectinate,
persulfate, phenylproprionate, picrate, pivalate, propionate,
succinate, tartrate, thiocyanate, tosylate and undecanoate. Other
examples of salts include anions of the compounds of the present
invention compounded with a suitable cation such as Na.sup.+,
NH.sub.4.sup.+, and NW.sub.4.sup.+ (wherein W is a C.sub.1-4 alkyl
group).
[0085] For therapeutic use, salts of the compounds of the present
invention will be pharmaceutically acceptable. However, salts of
acids and bases which are non-pharmaceutically acceptable may also
find use, for example, in the preparation or purification of a
pharmaceutically acceptable compound.
[0086] Esters of the prodrugs or compounds identified by the method
of this invention include carboxylic acid test (i.e.,
--O--C(.dbd.O)R) obtained by esterification of the 2'-, 3'- and/or
5'-hydroxy groups, in which R is selected from (1) straight or
branched chain alkyl (for example, n-propyl, t-butyl, or n-butyl),
alkoxyalkyl (for example, methoxymethyl), aralkyl (for example,
benzyl), aryloxyalkyl (for example, phenoxymethyl), aryl (for
example, phenyl optionally substituted by, for example, halogen,
C.sub.1-4alkyl, or C.sub.1-4alkoxy or amino); (2) sulfonate esters
such as alkylsulfonyl (for example, methanesulfonyl) or
aralkylsulfonyl; (3) amino acid esters (for example, L-valyl or
L-isoleucyl); (4) phosphonate esters and (5) mono-, di- or
triphosphate esters. The phosphate esters may be further esterified
by, for example, a C.sub.1-20 alcohol or reactive derivative
thereof, or by a 2,3di-(C.sub.6-24)acyl glycerol. In such esters,
unless otherwise specified, any alkyl moiety present
advantageously-contains from 1 to 18 carbon atoms, particularly
from 1 to 6 carbon atoms, more particularly from 1 to 4 carbon
atoms. Any cycloalkyl moiety present in such esters advantageously
contains from 3 to 6 carbon atoms. Any aryl moiety present in such
esters advantageously comprises a phenyl group. Examples of
lyxo-furanosyl prodrug derivatives of the present invention
include, for example, those with chemically protected hydroxyl
groups (e.g., with O-acetyl groups), such as
2'-O-acetyl-lyxo-furanosyl; 3'-O-acetyl-lyxo-furanosyl;
5'-O-acety-lyxo-furanosyl; 2',3'-di-O-acetyl-lyxo-furanosyl and
2',3',5'-ti-O-acetyl-lyxo-furanosyl.
[0087] Ethers of the compounds of the present invention include
methyl, ethyl propyl, butyl, isobutyl and sec-butyl ethers.
[0088] In a further embodiment, the substrate may not be chemically
related to pyrimidines or folates, but rather synthesized based
upon known parameters of rational drug design. See Dunn, W. J. et
al. (1996).
[0089] As is apparent to one skilled in the art, control cell
culture systems without drug and separately with a reference drug
such as the one exemplified below, also are assayed. Compounds
which preferentially kill target cells with about 2-fold and
preferably 3-fold or greater activity than normal cells are
preferred. This invention also provides the agents identified by
the methods described herein.
[0090] Tyrosine Kinases
[0091] The tyrosine kinase superfamily comprises the EGF receptor
(EGFR), the macrophage colony-stimulating factor (CSF-1) receptor
(v-fms), and the insulin receptor, which shows 30 to 40% identity
with the product of the ros oncogene. More specifically, the
members of this superfamily include v-src, c-src, EGFR, HER2, CSF-1
receptor, c-fms, v-ros, insilin receptor, and c-mos. See FIG. 8.5
of Burck, K. B. et al., eds. (1988). Overexpression of members of
the type 1 receptor tyrosine kinase superfamily has been documented
in many types of cancer (Eccles, S. A. et al. (1994-95)).
Overexpression of tyrosine kinases is linked to exposure to the
.alpha.-cancer biologic agent TNF-.alpha. (Hudziak, R. M. et al.
(1988) and Hudziak R. M. et al. (1990)) and to chemotherapy
(Stuhlinger et al. (1994)).
[0092] The transforming gene of the Rous sarcoma virus, v-src,
encodes an enzyme that phosphoryl tyrsine residues on proteins. The
c-src proto-oncogene is found on chromosome 20. Tissues and cell
lines derived from tumors of neuroectodermal origin having a neural
phenotype express high levels of c-src accompanied by high specific
kinase activity.
[0093] Several groups of investigators have reported overexpression
of c-erbB-2/neu ("HER2") oncogene in cancer cells. Brison (1993)
noted that erbB proto-oncogene is amplified in human tumors with
resultant overexpression in most cases. Amplification of the
c-erbB-2/neu oncogene has been reported in human mammary tumors
(Slamon, et al. (1987), van de Vijver et al. (1987), Pupa et al.
(1993), and Anderson et al. (1995)) and in blader tumors (Sauter et
al. (1993)), and in every case amplification was accompanied by
overexpression. c-erB-2/nea overexpression also has been reported
in ovarian cancer tissue samples (Slamin, et al. (1989), Meden et
al. (1994), and Felip et al. (1995)), and tumors derived from the
peripheral nervous system. Sukumar and Barbacid, (1990).
[0094] To perform the drug screening assay, tumor cell lines will
be assayed for expression of the oncogene or will be engineered to
express varying levels of tyrosine kinase. Selected cell lines arm
cultured and candidate drugs are added in varying concentrations.
The cells are assayed for cell killing or inhibition of cellular
proliferation, as described in Hudziak, R. M. et al. (1988) and
Hudziak, R. M. et al. (1990).
[0095] Dihydrofolate Reductase
[0096] Methotrexate is a potent inhibitor of dihydrofolate
reductase, an enzyme necessary for intracellular folate metabolism.
Dihydrofolate reductase functions to regenerate tetrahydrofolate
from dihydrofolate, a product of the thymidylate synthase reaction
(Voet, et al. eds. (1995), p. 813). It is was established that an
important mechanism of resistance of cells to methotrexate is an
increase in DHFR activity due to amplification of the DHFR gene.
Banerjee, D. et al. (1995), Schimke, R. T. et al. (1988). Lonn, U.
et al. (1996) reported that amplification of the DHFR gene occurred
in breast cancer patients who previously received adjuvant
chemotherapy (cyclophosphamide, methotrexate, 5-fluorouracil [CMF])
after surgery. Lack of the retinoblastoma (Rb) may also lead to
enhanced MTX resistance as a consequence of an increase in DHFR
mRNA expression activity without gene amplification. Li, W. W. et
al. (1995). Cell lines with mutated p53 have been shown to undergo
gene amplification, and the resistant cells are selected by
chemotherapy. Banerjee, D. et al. (1995), Yin, Y. et al. (1992) and
Livingston, L. R. et al. (1992). For the purposes of performing the
assay of this invention, Schimke, R. T. et al. (1988) describes
several mouse, hamster and human cell lines. Alternatively, the PCR
method of Lonn U. et al. (1996) is used to assay DHFR gene
amplification and identify cells that are useful in the method of
identifying therapeutic agents as described herein. The nucleotide
sequence of the cDNA coding for the human dihydrofolate reductase
is provided in Masters, J. N. and Attardi, G. (1983) and cells can
be engineered to express varying levels of the enzyme as noted
herein. Dicken, A. P. et al. (1993) describes a mutant DHFR gene
selected by chemotherapy. Purification of DHFR and assays related
to enzyme function are described in Nakano, T. et al. (1994).
Alternatively, cDNA encoding DHFR is transfected into NIH 3T3
cells. Candidate drugs are added in varying concentrations and cell
killing and inhibition of proliferation are assayed.
[0097] Antimetabolites dependent on dihydrofolate reductase
activity can be synthesized by the attachment of, for example, an
alkylating group to either the N5 or the C6 position of
dihydrofolate. Reduction of the N5-C6 bond by DHFR will result in
the release of the alkylating agent. In addition to the alkylating
groups, any moiety whose release by DHFR results in the production
of a toxin or an antimetabolite will be useful in the practice of
the invention.
[0098] Multidrug Resistant Tumors
[0099] Multidrug resistance (MDR) is a generic term for the variety
of strategies tumor cells use to evade the cytotoxic effects of
anticancer drug. MDR is characterized by a decreased sensitivity of
tumor cells not only to the drug employed for chemotherapy but also
to a broad spectrum of drugs with neither obvious structural
homology nor common targets. This phenotopic resistance is one of
the major obstacles to the successful treatment of tumors. MDR may
result from structural or functional changes at the plasma membrane
or within the cytoplasm cellular compartments, or nucleus.
Molecular mechanisms of MDR are discussed in terms of modifications
in detoxification and DNA repair pathways, changes in cellular
sites of drug sequestration, decreases in drug-target affinity,
synthesis of specific drug inhibitors within cells, altered or
inappropriate targeting of proteins, and accelerated removal or
secretion of drugs.
[0100] One of the mechanisms implicated in MDR results from
amplification and over-expression of a gene known as the
ATP-dependent multidrug resistant associated protein (MRP) in drug
selected cell lines. For a review of the mechanisms of MDR, see
Gottesman, M. M. et al. (1995) and Noder et al. (1996).
[0101] To establish MDR cell lines, drug selections are conducted
in either a single step or in multiple steps as described in
Gottesman, M. M. et al. (1995) and Simon, S. M. and Schindler, M.
(1994), and references cited therein. The isolation of DNA
sequences coding for MDR from various mammalian species is
described in Gros, P. et al. (1986), Gudkov, A. V. et al. (1987),
and Roninson, I. B. et al. (1984), and reviewed in Gottesman, M. M.
et al. (1995), and cells can be engineer to express varying levels
of this enzyme as described above. The prodrug targeting MDR will
be based upon the ATPase activity of this transporter.
[0102] Ribonucleotide Reductase
[0103] The ribonucleotide reductase reduces ribonucleotide
diphosphates to the corresponding deoxyribonucleoside diphosphates.
The enzyme is a tetramer made up of two .alpha.-subunits and two
.beta.-subunits. Hydroxyurea specifically blocks this reaction by
interacting with the tyrosyl free radical (Tyr-122) of the
.beta..sub.2-substrate complex. Voet et al. (1995). The goal in
targeting this reaction is to allow the accumulation of the free
radical product O.sub.2.sup.-, which is highly cytotoxic.
[0104] Application of Technology to Other Diseases
[0105] While the primary focus of this application is directed to
cancer, it should be recognize that the technology is broadly
applicable to other disease, especially antibiotic resistant
bacterial infections. The .beta.-lactam antibiotics encounter
resistance in bacteria as the result of overexpression of
.beta.-lactamases. Hamilton-Miller, J. M. T. and Smith, J. T. eds.
(1979) p. 443. Other enzymes, such as the aminoglycoside
phosphotransferase Type III, a induced and selected for following
treatment with aminoglycoside antibiotics, such as kanamycin.
McKay, G. A. et al. (1994). For the purpose of this application,
prodrug substrates derived from known substrates will be prepared
that will not block enzyme activity, but will instead take
advantage of the high enzyme activity to generate intracellular
toxins in the infectious agents.
[0106] In Vivo Administration
[0107] The in vitro assays are confirmed in animal models bearing
human tumors or infected with an antibiotic resistant microorganism
to determine in vivo efficacy.
[0108] Another aspect of this invention is a method for treating a
pathology characterized by hyperliferative cells in a subject
comprising administering to the subject a therapeutic amount of a
prodrug that is converted to a toxin in a hyperproliferative cell
by an endogenous intracellular enzyme as defined herein.
[0109] When the prodrug is administered to a subject such as a
mouse, a rat or a human patient, the agent can be added to a
pharmaceutically acceptable carrier and systemically or topically
administered to the subject. To determine patients that can be
beneficially treated a tumor sample is removed from the patient and
the cells are assayed for the level of expression of the enzyme of
interest. If the expression is above that expressed in normal cells
and an amount of the prodrug effective to kill or inhibit the cell
can be administered without undesirable side effects, then the
prodrug is a preferred embodiment. Therapeutic amounts can be
empirically determined and will vary with the pathology being
treated, the subject being treated and the toxicity of the
converted prodrug or cellular toxin. When delivered to an animal,
the method is useful to further confirm efficacy of the prodrug. As
an example of an animal model, groups of nude mice (Balb/co NCR
nu/nu female, Simonsen, Gilroy, Calif.) are each subcutaneously
inoculated with about 10.sup.3 to about 10.sup.9
hyperproliferative, cancer or target cells as defined herein. When
the tumor is established, the prodrug is administered for example,
by subcutaneous injection around the tumor. Tumor measurement to
determine reduction of tumor size are made in two dimensions using
venier calipers twice a week. Other animal models may also be
employed as appropriate. Lovejoy, et al. (1997) and Clarke, R.
(1996).
[0110] Administration in vivo cam be effected in one dose,
continuously or intermittently throughout the course of treatment.
Methods of determining the most effective means and dosage of
administration are well known to those of skill in the art and will
vary with the composition used for therapy, the purpose of the
therapy, the target cell being treated, and the subject being
treated. Single or multiple administrations can be carried out with
the dose level and pattern being selected by the treating
physicians. Suitable dosage formulations and methods of
administering the agents can be found below.
[0111] The agents and compositions of the present invention can be
used in the manufacture of medicaments and for the treatment of
humans and other animals by administration in accordance with
conventional procedures, such as an active ingredient in
pharmaceutical compositions.
[0112] The pharmaceutical compositions can be administered orally,
intranasally, parenterally or by inhalation therapy, and may take
the form of tablets, lozenges, granules, capsules, pills, ampoules,
suppositories or aerosol form. They may also take the form of
suspensions, solutions and emulsions of the active ingredient in
aqueous or nonaqueous diluents, syrups, granulates or powders. In
addition to a compound of the present invention, the pharmaceutical
compositions can also contain other pharmaceutically active
compounds or a plurality of compounds of the invention.
[0113] More particularly, a compound of the formula of the present
invention also referred to herein as the active ingredient, may be
administered for therapy by any suitable mute including oral,
rectal, nasal, topical (including transdermal, aerosol buccal and
sublingual), vaginal, parental (including subcutaneous,
intramuscular, intravenous and intradermal) and pulmonary. It will
also be appreciated that the preferred route will vary with the
condition and age of the recipient, and the disease being
treated.
[0114] In general, a suitable dose for each of the above-named
compounds, is in the range of about 1 to about 100 mg per kilogram
body weight of the recipient per day, preferably in the range of
about 1 to about 50 mg per kilogram body weight per day and most
preferably in the range of about 1 to about 25 mg per kilogram body
weight per day. Unless otherwise indicated, all weights of active
ingredient are calculated as the parent compound of the formula of
the present invention for salts or esters thereof, the weights
would be increased proportionately. The desired dose is preferably
presented as two, three, four, five, six or more sub-doses
administered at appropriate intervals throughout the day. These
subdoses may be administered in unit dosage forms, for example,
containing about 1 to about 100 mg, preferably about 1 to above
about 25 mg, and most preferably about 5 to above about 25 mg of
active ingredient per unit dosage form. It will be appreciated that
appropriate dosages of the compounds and compositions of the
invention may depend on the type and severity and stage of the
disease and can vary from patient to patient. Determining the
optimal dosage will generally involve the balancing of the level of
therapeutic benefit against any risk or deleterious side effects of
the treatments of the present invention.
[0115] Ideally, the prodrug should be administered to achieve peak
concentrations of the active compound at sites of disease. This may
be achieved, for example, by the intravenous injection of the
prodrug, optionally in saline, or orally administered for example,
as a tablet, capsule or syrup containing the active ingredient.
Desirable blood levels of the prodrug may be maintained by a
continuous infusion to provide a therapeutic amount of the active
ingredient within disease tissue. The use of operative combinations
is contemplated to provide therapeutic combinations requiring a
lower total dosage of each component antiviral agent than may be
required when each individual therapeutic compound or drug is used
alone, thereby reducing adverse effects.
[0116] While it is possible for the prodrug ingredient to be
administered alone, it is preferable to present it as a
pharmaceutical formulation comprising at least one active
ingredient, as defined above, together with one or more
pharmaceutically acceptable carriers therefor and optionally other
therapeutic agents. Each carrier must be "acceptable" in the sense
of being compatible with the other ingredients of the formulation
and not injurious to the patient.
[0117] Formulations include those suitable for oral, rectal, nasal,
topical (including transdermal, buccal and sublingual), vaginal,
perenteral (including subcutaneous, intramuscular, intravenous and
intradermal) and pulmonary administration. The formulations may
conveniently be presented in unit dosage form and may be prepared
by any methods well known in the art of pharmacy. Such methods
include the step of bringing into association the active ingredient
with the carrier which constitutes one or more accessory
ingredients. In general, the formulations art prepared by uniformly
and intimately bringing into association the active ingredient with
liquid carriers or finely divided solid carriers or both, and then
if necessary shaping the product.
[0118] Formulations of the present invention suitable for oral
administration may be presented as discrete units such as capsules,
cachets or tablets, contain a predetermined amount of the active
ingredient; as a powder or granules; as a solution or suspension in
an aqueous or non-aqueous liquid; or as an oil-in-water liquid
emulsion or a water-in-oil liquid emulsion. The active ingredient
may also be presented a bolus, electuary or paste.
[0119] A tablet may be made by compression or molding, optionally
with one or more accessory ingredients. Compressed tablets may be
prepared by compressing in a suitable machine the active ingredient
in a fee-flowing from such as a powder or granules, optionally
mixed with a binder (e.g., povidone, gelatin, hydroxypropylmethyl
cellulose), lubricant, inert diluent, preservative, disintegrate
(e.g., sodium starch glycolate, crosslinked povidone, cross-linked
sodium carboxymethyl cellulose) surface-active or dispersing agent.
Molded tablets may be made by molding in a suitable machine a
mixture of the powdered compound moistened with an inert liquid
diluent. The tablets may optionally be coated or scored and may be
formulated so as to provide slow or controlled release of the
active ingredient therein using, for example, hydroxypropylmethyl
cellulose in varying proportions to provide the desired release
profile. Tablets may optionally be provided with an enteric
coating, to provide release in pans of the gut other than the
stomach
[0120] Formulations suitable for topical administration in the
mouth include lozenges comprising the active ingredient in a
flavored basis, usually sucrose and acacia or tragacanth; pastilles
comprising the active ingredient in an inert basis such as gelatin
and glycerin, or sucrose and acacia; and mouthwashes comprising the
active ingredient in a suitable liquid carrier.
[0121] Pharmaceutical compositions for topical administration
according to the present invention may be formulated as an
ointment, cream, suspension, lotion, powder, solution, paste, gel,
spray, aerosol or oil. Alternatively, a formulation may comprise a
patch or a dressing such as a bandage or adhesive plaster
impregnated with active ingredients and optionally one or more
excipients or diluents.
[0122] For diseases of the eye or other external tissue, e.g.,
mouth and skin, the formulations are preferably applied as a
topical ointment or cream containing the active ingredient in an
amount of for example, about 0.075 to about 20% w/w, preferably
about 0.2 to about 25% w/w and most preferably about 0.5 to about
10% w/w. When formulated in an ointment, the prodrug may be
employed with either a paraffinic or a water-miscible ointment
base. Alteratively, the prodrug ingredients may be formulated in a
cream with an oil-in-water cream base.
[0123] If desired, the aqueous phase of the cream base may include,
for example, at least about 30% w/w of a polyhydric alcohol, i.e.,
an alcohol having two or more hydroxyl groups such as propylene
glycol, butane-1,3-diol, mannitol, sorbitol, glycerol and
polyethylene glycol and thereof. The topical formulations may
desirably include a compound which enhances absorption or
penetration of the prodrug ingredient through the skin or other
affected areas. Examples of such dermal penetration enhance include
dimethylsulfoxide and related analogues.
[0124] The oily phase of the emulsions of this invention may be
constituted from known ingredients in an known manner. While this
phase may comprise merely an emulsifier (otherwise known as an
emulgent), it desirably comprises a mixture of at lease one
emulsifier with a fat or an oil or with both a fat and an oil.
Preferably, a hydrophilic emulsifier is included together with a
lipophilic emulsifier which acts as a stabilizer. It is also
preferred to include both an oil and a fat. Together, the
emulsifier(s) with or without stabilizer(s) make up the so-called
emulsifying wax, and the wax together with the oil and/or fat make
up the so-called emulsifying ointment base which forms the oily
dispersed phase of the cream formulations.
[0125] Emulgents and emulsion stabilizers suitable for use in the
formulation of the present invention include Tween 60, Span 80,
cetosearyl alcohol, myristyl alcohol, glyceryl monostearate and
sodium lauryl sulphate.
[0126] The choice of suitable oils or fats for the formulation is
based on achieving the desired cosmetic properties, the solubility
of the active compound in most oils likely to be used in
pharmaceutical emulsion formulations is very low. Thus the cream
should preferably be a non-greasy, non-staining and washable
product with suitable consistency to avoid leakage from tubes or
other containers. Straight or branched chain mono- or dibasic alkyl
esters such as di-isoadipate, isocetyl stearate, propylene glycol
diester of coconut fatty acids, isopropyl myristate, decyl oleate,
isopropyl palmitate, butyl irate, 2-ethylhexyl palmitate or a blend
of blanched chain esters known as Crodamol CAP may be used, the
last three being preferred esters. These may be used alone or in
combination depending on the properties required. Alternatively,
high melting point lipids such as white soft paraffin and/or liquid
paraffin or other mineral oils can be used.
[0127] Formulations suitable for topical administration to the eye
also include eye drops wherein the active ingredient is dissolved
or suspended in a suitable carrier, especially an aqueous solvent
for the prodrug ingredient. The prodrug ingredient is preferably
present in such formulation in a concentration of about 0.5 to
about 20%, advantageously about 0.5 to about 10% particularly about
1.5% w/w.
[0128] Formulations for rectal administration may be presented as a
suppository with a suitable base comprising, for example, cocoa
butter or a salicylate.
[0129] Formulations suitable for vagina administration may be
presented as pessaries, tampons, creams, gels, pastes, foams or
spray formulations containing in addition to the prodrug
ingredient, such carriers as are known in the art to be
appropriate.
[0130] Formulations suitable for nasal administration, wherein the
carrier is a solid, include a coarse powder having a particle size,
for example, in the range of about 20 to about 500 microns which is
administered in the manner in which snuff is taken, i.e., by rapid
inhalation through the nasal passage from a container of the powder
held close up to the nose. Suitable formulations wherein the
carrier is a liquid for administration as, for example, nasal
spray, nasal drops, or by aerosol administration by nebulizer,
include aqueous or oily solutions of the prodrug ingredient.
[0131] Formulations suitable for parenteral administration include
aqueous and non-aqueous isotonic sterile injection solutions which
may contain anti-oxidants, buffers, bacteriostats and solutes which
render the formulation isotonic with the blood of the intended
recipient; and aqueous and non-aqueous sterile suspensions which
may include suspending agents and thickening agents, and liposomes
or other microparticulate systems which are designed to target the
compound to blood components or one or more organs. The
formulations may be presented in unit-dose or multi-dose sealed
contains, for example, ampoules and vials, and may be stored in a
freeze dried (lyophilized) condition requiring only the addition of
the sterile liquid carrier, for example water for injections,
immediately prior to use. Extemporaneous injection solutions and
suspensions may be prepared from sterile powders, ganules and
tablets of the kind previously described.
[0132] Preferred unit dosage formulations are those containing a
daily dose or unit, daily subdose, as herein above-recited, or an
appropriate faction thereof, of a prodrug ingredient.
[0133] It should be understood that in addition to the ingredients
particularly mentioned above, the formulations of this invention
may include other agents conventional in the an having regard to
the type of formulation in question, for example, those suitable of
oral administration may include such further agents as sweeteners,
thickeners and flavoring agents.
[0134] Prodrugs and compositions of the formula of the present
invention may also be presented for the use in the form of
veterinary formulations, which may be prepared, for example, by
methods that are conventional in the art.
EXAMPLES
[0135] The following examples are specifically directed to the
target enzyme TS. It is apparent to those skilled in the art that
the following methods can be modified for the discovery of other
prodrugs to target enzymes as defined herein.
[0136] Chemical and Cell-Based Assays
[0137] Pyrimidine-based prodrugs are chosen based on the ability to
react with intracellular thymidylate synthase, and release the
toxin into the medium without containing the enzyme. Candidate drug
are screened in reaction mixtures containing human thymidylate
synthase with and without N5N10-methylenetetrahydrofolate, and the
candidate prodrug. The leaving group of the candidate prodrug
(e.g., at the pyrimidine 5 position) is labeled, for example, with
tritium using methods well known in the art. The control substrate
is similarly labeled (e.g. 5-.sup.3H) dUMP, under the same reaction
conditions. The assays are done similarly to the description
provided in Carreras, C. W. and Santi, D. V. (1995), and references
cited therein. The human thymidine synthase can be purified from E.
coli containing the expressed human thymidylate synthase. See
Davisson, V. J. et al. (1989) and Davisson, V. J. et al. (1994).
This approach provides a scaleable assay capable of screening large
numbers of candidate compounds.
[0138] A high throughput screen to identify biologically active
compounds is outlined in FIGS. 3, 4 and 5. The basis of the test is
the ease of genetic manipulation and growth of E coli, and similar
single cell organisms (e.g. yeast), see Miller (1992) and Spector,
et al. (1997). The key step is g the endogenous enzyme activity
corresponding to an enzyme target for prodrug design. This can be
done by any of the methods described by Miller (1992), Sambrook
(1989) or Spector et al. (1997). These methods include chemical and
biologic (e.g. viral or t on insertional) mutagenesis, followed by
an appropriate selection procedure The TS negative (TS) cell then
becomes a negative control for the identification of prodrugs that,
when acted upon by thymidylate synthase, become cell toxins. A
similar approach can be made with other cell types, e.g. other
bacteria, yeast or other selectable single cell organisms. In the
assay, both control and recombinant organisms are compared for
sensitivity to the test compounds. As will be understood by those
skilled in the art, prodrugs which distinguish between species of
enzyme can also be derived from this procedure. For example,
otherwise identical cells expressing hunk and yeast enzymes can be
used to detect antibiotic prodrugs which are preferentially toxic
only to the cells expressing the yeast enzyme. In this way, novel
and specific antibiotics can be discovered.
[0139] Example cell lines are ras-transformed NIH 3T3 cells
(obtained from the ATCC) and are engineered to express increasing
quantities of human thymidylate synthase (Hu TS) from the cloned
cDNA. Transfection is done in a transient or permanent basis (see
Chen, L. et al. (1996), Hudziak R. M. et al. (1988), and Carter, P.
et al. (1992). NIH-000 (ras-transformed parent cell line); NIH-001
(low expresser of HuTS); NIH-002 (intermediate expressor of Hu TS);
NIH-003 (high expressor of HuTS). The level of expression of TS in
each cell line is monitored by immunoblot and enzyme assay in cell
substrates, using antibody directed versus HuTS protein for
immunodetection (e.g., as described in Chen, L. et al. (1996)).
Enzymatic assays are performed as reviewed by Carreras, C. W. and
Santi, D. N. (1995).
[0140] Human colorectal and breast tumor cell lines are screened
for expression of HuTS enzyme. Cell lines expressing low, moderate
and high levels of HuTS will be exposed to drug candidates as
described above for the NIH 3T3 cell lines. Growth inhibition and
cytotoxicity are monitored as described above. Similar tests can be
carried out for each of the enzymes listed in Table 1.
[0141] In Vivo Testing
[0142] Ras-transformed NIH 3T3 cell lines are transplanted
subcutaneously into immudeficient mice. Initial therapy may be
direct intratumoral injection. The expected result is that
increased level of expression of HuTS or a target enzyme leads to
enhanced antitumor activity by the drug candidates. Similar studies
are performed with human tumors expressing increasing levels of
HuTS or a target enzyme, and demonstrating N efficacy in response
to drug correlates with their level of HuTS expression or target
enzyme. Optionally, experiments are be performed as above except
the drug will be administered intravenously into the animals to
address issues related to efficacy, toxicity and pharmacobiology of
the drug candidates.
[0143] The in vivo studies will be conducted as described by
Harris, M P et al. (1996) and Antelman, D. et al. (1995).
[0144] While the invention has been described in detail herein and
with reference to specific embodiments thereof, it will be apparent
to one skilled in the art that various changes and modifications
can be made to the invention as described above without departing
from spirit and scope of.
REFERENCES
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